Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Deferred Revenue (Details)

v3.10.0.1
Summary of Significant Accounting Policies - Deferred Revenue (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]            
Power purchase or lease agreement term     20 years      
Deferred revenue $ 586,434   $ 586,434   $ 564,852 $ 525,400
Deferred revenue, revenue recognized 13,300 $ 12,100 39,100 $ 35,100    
Contracted but not yet recognized 5,100,000   $ 5,100,000      
Revenue expected to recognize over next twelve months, percent     6.00%      
Revenue recognized, term, existing deferred revenue     20 years      
Under Customer Agreements            
Deferred Revenue Arrangement [Line Items]            
Deferred revenue 571,024   $ 571,024   548,280  
Under Customer Agreements | Payments received            
Deferred Revenue Arrangement [Line Items]            
Deferred revenue 535,045   535,045   517,544  
Under Customer Agreements | Financing component balance            
Deferred Revenue Arrangement [Line Items]            
Deferred revenue 35,979   35,979   30,736  
Under SREC contracts            
Deferred Revenue Arrangement [Line Items]            
Deferred revenue 15,410   15,410   16,572  
Under SREC contracts | Payments received            
Deferred Revenue Arrangement [Line Items]            
Deferred revenue 13,494   13,494   14,805  
Under SREC contracts | Financing component balance            
Deferred Revenue Arrangement [Line Items]            
Deferred revenue $ 1,916   $ 1,916   $ 1,767